1. Field of the Invention
The present invention relates to an ink preferably usable for ink-jet recording which records on recording material while discharging ink drops from orifices in response to recording signals as well as an ink set, an ink cartridge, a recording unit, an image recording apparatus and an image recording method which use the ink.
2. Related Background Art
There has conventionally been reported or proposed inks having various compositions as those which are used for ink-jet recording. In the recent years in particular, inks have been studied and examined in details in various aspects such as compositions and physical properties thereof in order to perform favorable recording on plain paper such as copying paper, reporting paper, notebooks, letter paper or the like which are generally used in offices as well as cloths.
Also for ink-jet recording method, there have been proposed various modes including one which continuously produces electrically charged liquid drops and uses a portion of the liquid drops for recording, another which transmits signals to a recording head having a piezoelectric element and performs recording by discharging recording liquid in response to the signals, and still another which provides heat energy corresponding to recording signals to the recording liquid contained in a chamber in a recording head and performs recording by discharging the recording liquid. For example, Japanese Patent Application Laid-Open No. 54-59936 discloses an ink-jet recording method in which an ink is discharged by utilizing ink bubbling phenomenon caused by heat energy. The method facilitates to highly integrate openings through which the ink is discharged (hereinafter referred to as orifices) or to arrange the orifices at a high density, and thereby it is adopted as one of main current ink-jet recording methods. As one of preferable characteristics for the ink for the ink-jet recording, there can be mentioned a characteristic to prevent, as far as possible, the orifices from clogging, which may cause improper ink discharge or non-discharge of the ink when recording is restarted after interruption of the recording.
As a current trend regarding an ink jet recording method, intensive reserch and development are being conducted to achieve much smaller diameter of orifices in order to meet a demand for a higher quality images. In addition, as ink-jet recording apparatus prevails, environments for use thereof are being diversified. On the basis of researches so far made, the inventors of the present invention recognized that it was important to adapt the aforementioned ink characteristics for the trend and the diversification for more stable ink-jet recording.
On the basis of this recognition, the inventors repeatedly examined ink containing water-soluble coloring materials (for example, an ink which contains a water-soluble coloring material and a water-soluble organic solvent such as glycol, that is, an ink which is mainly used currently as ink composition and has compositions containing water-soluble coloring materials). As a result, the inventors found that the ink can be hardly discharged or tends to cause inaccurate redischarge phenomena (for example, a phenomenon to deviate ink attaining points or a phenomenon to splash ink) after recording interruption when, for example, temperature is low or diameters of orifices are smaller. Though a reason for this tendency is not clarified, the examination so far made provided results that components such as water which have relatively low vapor pressures of the aqueous ink are vaporized through the orifices from the aqueous ink contained in the orifices, whereby concentration of the components such as water-soluble organic solvents which have relatively high vapor pressures rises in the ink contained in the orifices, and in case that the water-soluble coloring material has higher affinity with an organic solvent than that of water, it is presumed that concentration of the coloring material in the aqueous ink contained in the orifices becomes higher than expected concentration resulting from the vaporization of water or the like, whereby a viscosity of the ink contained in the orifices becomes higher than a level anticipated by those skilled in the art. It is considered that the unexpected rise in concentration of the coloring material makes difficulty in the ink redischargeability conspicuous when the head placed in a low temperature environment in which a viscosity of the ink is further enhanced or on the recording head provided with smaller whose orifices discharging force is relatively weakened.
An object of the present invention is therefore to provide an ink which can rarely be not redischarged from orifices after a pause of recording even in diversified environment for use or even when diameters of orifices are further reduced.
Another object of the present invention is to provide an image recording method which is capable of stably forming high quality images even in diversified environments for use or stably exhibiting its effect even when diameters of orifices are finely reduced to enhance qualities of recorded images.
A further object of the present invention is to provide an image forming apparatus which is capable of stably recording high quality images even in diversified environments for use or stably exhibiting its effect even when diameters of orifices are finely reduced to enhance qualities of images as well as an ink cartridge, an ink set and a recording unit which are usable with the image forming apparatus.
According to a first aspect of the present invention, there is provided an ink containing a water-soluble coloring material and an aqueous solvent, wherein the ink further contains bis-hydroxyethyl sulfon and wrea.
According to further aspect of the present invention, there is provided an image recording method comprising a step of imparting an ink to an image forming region of a recording medium, wherein the ink contains a water-soluble coloring material, bis-hydroxyethyl sulfone and urea in an aqueous solvent.
According to further aspect of the present invention, there is provided an image recording apparatus comprising a recording unit which comprises an ink housing section containing an ink, means for imparting the ink to a recording medium, means for supplying said ink to said means, and means for operating the means for imparting the recording ink to the recording medium in response to record signal wherein the ink contains a water-soluble coloring material, bis-hydroxyethyl sulfone and urea in an aqueous solvent.
According to further aspect of the present invention, there is provided an ink set comprising a combination of a first ink containing a first water-soluble coloring material, bis-hydroxyethyl sulfone and urea in an aqueous solution, and a second ink containing a second coloring material, wherein the first and second coloring materials have colors which are selected from the group consisting of yellow, magenta, cyan, black, red, blue and green.
According to further aspect of the present invention, there is provided an ink cartridge comprising an ink housing section containing an ink, wherein said ink contains a water-soluble coloring material, bis-hydroxyethyl sulfone and urea in an aqueous solvent.
According to further aspect of the present invention, there is provided a recording unit comprising an ink housing section containing an ink, means for imparting an ink to a recording medium and means for supplying the ink to the means for imparting an ink to a recording medium wherein the ink contains a water-soluble coloring material, bis-hydroxyethyl sulfone and urea in an aqueous solvent.
According to these embodiments of the present invention, it is possible to stabilize redischargeability of the aqueous ink containing a water-soluble coloring material in diversified recording environments even when diameters of orifices are finely reduced.
According to further aspect of the present invention, there is provided an image recording method comprising the steps of: providing an image recording apparatus comprising a) a recording unit provided with i) an ink housing section containing an ink, ii) a recording head for ejecting the ink from an orifice to a recording medium, and iii) means for supplying the ink from the ink housing section to the recording head; and b) means for operating the recording head to eject the ink to a recording medium in response to a recording signal; and operating the image recording apparatus, discharging the ink from an orifice and adhering the ink to an image recording region on a recording medium, wherein the ink contains a water-soluble coloring material, bis-hydroxyethyl sulfone and urea in an aqueous medium, and wherein the orifice has a size capable of ejecting 0.1 to 40 picoliters of an ink with one ejection operation.
This embodiment makes it possible to stably record highly minute images.
According to further aspect of the present invention, there is provided an image recording apparatus comprising: a) a recording unit provided with i) an ink housing section containing an ink, ii) a recording head for ejecting an ink from an orifice to a recording medium, and iii) means for supplying the ink in the ink housing section to the recording head; and b) means for allowing the recording unit to eject the ink in response to a recording signal, wherein the ink contains a water-soluble coloring material, bis-hydroxyethyl sulfone and urea in an aqueous medium, and the orifice has a size capable of ejecting 0.1 to 40 picoliters of an ink with one ejection operation.
According to still further aspect of the present invention, there is provided a recording unit comprising an ink housing section containing an ink which contains a water-soluble coloring material, bis-hydroxyethyl sulfone and urea in an aqueous solvent, a recording head for discharging the recording ink from an orifice to a recording medium, and means for supplying the ink in the ink housing section for the recording head: the orifice has a size capable of discharging 0.1 to 40 picoliters of ink with a single discharging operation.
These embodiments makes it possible to stable recording of an image having a remarkably high quality.
Though a reason that each of the objects of the present invention can be accomplished by adopting each of the embodiments described above is not clear, it is considered that bis-hydroxyethyl sulfone is a solid at normal temperature and tends to be separated in a wax like condition when it is contained in the aqueous medium at a ratio exceeding 80 wt %, whereby this phenomenon occurs microscopically also in the ink contained in orifices as water is vaporized. Further, urea remarkably enhances an affinity between water and a water-soluble dye, thus, it is considered that coexistence of bis-hydroxyethyl sulfone and urea multiplies an effect to suppress vaporization of water in ink from the orifices due to separation of BHES in the ink contained in the orifices by an effect to suppress abrupt enhancement of a dye concentration in ink in the vicinities of the orifices.
Japanese Patent Application Laid-Open No. 6-271798 discloses an ink containing bis-hydroxyethyl sulfone, and discloses that bleeding and slow drying characteristic of the ink on recording media (for example, papers, cloths or the like) are improved when an ink-jet recording is conducted by using the ink. Further the ink is said to have enhanced ejection stability. However, this patent is devoid of any disclosure about the technical problems described above, and the present invention does not teach or suggest the effect obtainable with the ink of the present invention.
Furthermore, Japanese Patent Application Laid-Open No. 8-127981 discloses ink for textile printing by an ink jet method which contains a dispersed dye and an aqueous medium and to which bis-hydroxyethyl sulfone and a derivative thereof are added. In addition, it is described that urea may be added. Above-mentioned technical problem is not disclosed, however, this patent also makes no reference even to the technical problems described above not to speak of the ink according to the present invention nor suggests the effect obtainable with the ink.